| Nanoparticle thermometry and pressure sensors -> Monitor Keywords |
|
|
  Nanoparticle thermometry and pressure sensorsUSPTO Application #: 20070189359Title: Nanoparticle thermometry and pressure sensors Abstract: A nanoparticle fluorescence (or upconversion) sensor comprises an electromagnetic source, a sample and a detector. The electromagnetic source emits an excitation. The sample is positioned within the excitation. At least a portion of the sample is associated with a sensory material. The sensory material receives at least a portion of the excitation emitted by the electromagnetic source. The sensory material has a plurality of luminescent nanoparticles luminescing upon receipt of the excitation with luminance emitted by the luminescent nanoparticles changing based on at least one of temperature and pressure. The detector receives at least a portion of the luminance emitted by the luminescent nanoparticles and outputs a luminance signal indicative of such luminance. The luminescence signal is correlated into a signal indicative of the atmosphere adjacent to the sensory material. (end of abstract)
Agent: Dunlap, Codding & Rogers P.C. - Oklahoma City, OK, US Inventors: Wei Chen, Shaopeng Wang, Sarah Westcott USPTO Applicaton #: 20070189359 - Class: 374161000 (USPTO) Related Patent Categories: Thermal Measuring And Testing, Temperature Measurement (e.g., Thermometer), Nonelectrical, Nonmagnetic, Or Nonmechanical Temperature Responsive Property, Change Of Optical Property The Patent Description & Claims data below is from USPTO Patent Application 20070189359. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] The present application is a continuation of U.S. Ser. No. 10/460,531 filed on Jun. 12, 2003 which claims priority under 35 U.S.C. .sctn.119(e) to the provisional patent application identified by U.S. Ser. No. 60/388,211 filed Jun. 12, 2002. The present patent application is also a continuation-in-part and claims priority under 35 U.S.C. .sctn.120 to non-provisional patent application identified by U.S. Pat. No. 7,008,559 issued on Mar. 7, 2006 and entitled "Upconversion Luminescence Materials and Methods of Making and Using Same." BACKGROUND OF INVENTION [0002] Temperature is a fundamental property and its measurement is often required for both scientific research and industrial applications. For industrial manufacturing, real-time temperature monitoring can be used to optimize processing, minimizing waste and energy consumption. Spatially resolved temperature monitoring can establish regions of an integrated circuit in which heat builds up and suggest improvements in design of the circuit or its cooling system. Monitoring the temperature of high speed moving parts, such as turbine blades, can identify changes that signify a developing weakness in the blade. In bioengineering and biochemistry, temperature changes of even a few degrees can mean the difference between life and death for a cell. [0003] Traditional methods of measuring temperature include thermocouples, thermistors, resistance temperature detectors (RTDs), and measurement of emitted infrared light. Thermistors, thermocouples, and RTDs all require electrical wiring, which is not suitable for applications in which electromagnetic noise is strong, sparks could be hazardous, the environment is corrosive, or parts are rapidly moving. In another approach, temperature can be determined from a measurement of the infrared light that is emitted from a hot sample. Infrared measurements have two essential flaws in sample comparison and common interferants. One can either assume that the sample emits at the same rate as a blackbody or for an accurate determination of temperature, the emissivity of the material must be known. For thermal imaging, the emissivity must be constant for all objects in the image. In addition, the infrared wavelengths typically used in determining temperature are absorbed by water vapor and by ordinary glass materials, preventing measurements through windows. [0004] By using the fluorescence from luminescent materials to determine temperature, many of the problems and limitations of above methods can be avoided. Fluorescence from luminescent materials is known to depend on temperature in several ways. As the temperature of the phosphor is changed, the intensity of the fluorescence, the decay lifetime of the fluorescence, and the wavelength (or energy) of the fluorescence may all change. Because the fluorescence can be both excited and measured optically, fluorescence-based temperature sensors are advantageous compared to thermocouples in applications where electromagnetic noise is strong, electric wires might be hazardous, or it is physically difficult to connect a wire for instance in spinning centrifuges in turbines, or in wind tunnels. [0005] Conventional phosphors are made from crystalline semiconductor materials and typically have grain sizes of several microns. These grains are mixed with a binder material and coated on the surface of a part whose temperature is to be measured. The grain size limits resolution by scattering both the excitation light and emitted light. It also imposes a minimum thickness of phosphor coating of several microns on the sample. Thick coatings are disadvantageous because the phosphor coating may act as an insulating layer on the part's surface, giving results for temperature that cannot be applied to similar uncoated parts. Also, the thermal mass is greater for thicker coatings. This introduces a delay in making temperature measurements while the sensor comes to thermal equilibrium with what it is measuring. Another approach to temperature sensing is to dope optical fibers, generally with rare earth ions, and observe the fluorescence of the dopants. There is a limited selection of materials for this approach. [0006] Nanoparticles have enhanced emission efficiencies and faster decay times than bulk materials. In addition, their small size and the ultrathin films that can be made from nanoparticles enable high sensitivity, accuracy, and spatial resolution. Their small size means that they have a low thermal mass and can respond quickly to temperature changes. Their fast decay times are also required for a quick response to temperature changes. [0007] Several temperature sensors using electrical measurements of nanoparticles have been developed. The Coulomb blockade thermometer (CBT) is based on the temperature dependence of electric conductance characteristics of tunnel junction arrays. The arrays are nanofabricated on nitridized or oxidized silicon substrate by electron beam lithography. The overall size of the sensor tip is in the sub-millimeter range. The application of this kind of thermometer is focused on cryogenic temperature monitoring, and the thermometer has been found insensitive to high magnetic fields. However, the temperature sensing only works at temperatures below 100 K. [0008] Similar to temperature, pressure is also a fundamental property and its measurement is important for scientific research, medical, military and industrial applications. Conventionally, pressure is measured using manometers and through flow versus velocity measurements. Both are examples of pressure sensing on large scale items like reactors and pipes. Pressure is also measured based on the displacement of a diaphragm or using piezoelectric materials. [0009] The pressure behaviors of phosphors are also similar to that of temperature, both related to the changes in crystal field or chemical bond-length. When temperature increases, the crystal field is weaker and the chemical bond is longer, whereas, when pressure increases, the crystal field is stronger and the chemical bond is shorter. Accordingly, the luminescence trends of temperature and pressure are different. Both temperature and pressure sensors can be designed and fabricated based on these dependencies. [0010] Broadly, the present invention provides a method for using luminescence from nanoparticles to measure temperature or pressure; a method for using fluorescent resonant energy transfer from nanoparticles to measure temperature or pressure; and a method for using upconversion luminescence from nanoparticles to measure temperature or pressure. SUMMARY OF THE INVENTION [0011] Temperature and pressure can be determined by measuring fluorescent properties such as the intensity, the decay lifetime, or the wavelength. Using nanoparticles, particles with dimensions of less than 1000 nm, as the fluorescent material offers advantages for fluorescence-based thermometry such as higher resolution, incorporation into a variety of media, thinner coating layers, lower cost, and higher sensitivity. The energy transfer rate from a donor to an acceptor is temperature and/or pressure dependent. As a result, the luminescence from a donor-acceptor pair is sensitive to temperature and/or pressure changes. This allows one to design and fabricate an energy transfer system for temperature and/or pressure sensors, including a system composed of two sizes or two kinds of nanoparticles; or one nanoparticle or one host with two emitters. Thermometry or temperature imaging is also possible using the temperature-dependent upconversion luminescence of nanoparticles. An upconversion temperature sensor or upconversion imaging might have higher resolution and/or sensitivity because the luminescence background is much lower than in fluorescence. [0012] Using nanoparticles for temperature sensors or nanothermometry or nanothermometers may overcome the limitations of conventional phosphors as mentioned above. Luminescent nanoparticles with high quantum efficiency make it possible to design and fabricate more sensitive temperature sensors. It is known that oscillator strength is a very important optical parameter that determines the absorption cross-section, recombination rate, luminescence efficiency, and the radiative lifetime in materials. The oscillator strength of the free exciton is given by the formula: f ex = 2 .times. .times. m .eta. .times. .DELTA. .times. .times. E .times. .times. .mu. 2 .times. U .function. ( 0 ) 2 where m is the electron mass, .DELTA.E is the transition energy, .mu. is the transition dipole moment, and |U(0)|.sup.2 represents the probability of finding the electron and hole at the same site (the overlap factor). In nanostructured materials, the electron-hole overlap factor increases largely due to the quantum size confinement, thus yielding an increase in the oscillator strength. The oscillator strength is also related to the electron-hole exchange interaction that plays a key role in determining the exciton recombination rate. In bulk semiconductors, due to the extreme dislocation of the electron or hole, the electron-hole exchange interaction term is very small; while in molecular-size nanoparticles, due to the confinement, the exchange term should be very large. Therefore, one may expect a large enhancement of the oscillator strength from bulk to nanostructured materials. [0013] In doped semiconductors, excitons are bound to impurity centers. The oscillator strength is given by the formula:f=f.sub.ex|.intg.dxF(x)|.sup.2/.OMEGA..sub.mol where f.sub.ex is the oscillator strength of the free exciton and .OMEGA..sub.mol is the volume of one molecule. The oscillator strength of a bound exciton is actually given by f.sub.ex multiplied by the number of molecules covered by the overlap of the electron and hole wave functions. Clearly, quantum size confinement will also enhance the bound exciton oscillator strength in doped nanoparticles. The luminescence efficiency is also proportional to the exciton oscillator strength; therefore, it can be enhanced via quantum size confinement. Strong evidences for the above theory are from our observations on ZnS:Mn.sup.2+ nanoparticles as reported in W. Chen, R. Sammynaiken, Y. Huang, J. Appl. Phys. Luminescence Enhancement of ZnS:Mn Nanoclusters in Zeolite, 2000, 88, 5188 (2000) and EuS, W. Chen, X. H. Zhang, Y. Huang, Luminescence Enhancement of EuS Clusters in USY-Zeolite, Appl. Phys. Lett., 76 (17): 2328-2330 (2000). The luminescence intensity of the 1 nm sized ZnS:Mn.sup.2+ nanoparticles in zeolite-Y was reported to be much stronger than other nanoparticles in W. Chen, R. Sammynaiken, Y. Huang, J. Appl. Phys. Luminescence Enhancement of ZnS:Mn Nanoclusters in Zeolite, 2000, 88, 5188 (2000). More interesting is that bulk EuS at room temperature is reported as not luminescent but strong luminescence was observed when EuS nanoparticles were formed in zeolite (see W. Chen, X. H. Zhang, Y. Huang, Luminescence Enhancement of EuS Clusters in USY-Zeolite, Appl. Phys. Lett., 76 (17): 2328-2330 (2000)). [0014] The radiative decay lifetime (.tau.) which is closely related to the oscillator strength of a transition, is represented by the formula:.tau.=4.5(.lamda..sub.A.sup.2/nf) where n is the refractive index and .lamda..sub.A is the wavelength. Thus, the lifetime is shortened with decreasing size due to the increase of the oscillator strength, f. High efficiency with short decay times makes nanoparticles good candidates for luminescence based temperature sensors. [0015] It is generally accepted that the major non-radiative energy relaxation channel in semiconductors is due to thermal quenching, also known as phonon quenching. The density of phonons increases with temperature, increasing the non-radiative relaxation rate and therefore in effect decreasing the amount of fluorescent light. If the phonon coupling is stronger, the non-radiative rate is higher and the luminescence is more sensitive to temperature change. Based on the theory of phonon quenching, the temperature dependence of the emission intensity, I(T), can be determined by the formula: I .function. ( T ) = I 0 1 + a .times. .times. e - E b / KT ( 1 ) where E.sub.b is the activation energy (thermal quenching energy), K is the Boltzmann constant, a is a constant related to the ratio of the non-radiative rate to the radiative rate, and I.sub.0 is the emission intensity at 0 K. Excellent agreement between theory and experiment in most cases suggests that the intensity decrease of a nanoparticle (or phosphor) with a single emitting center is due to thermal quenching. Note that this thermal quenching is a reversible process. [0016] With some nanoparticles, an enhancement in intensity or an irreversible change will be seen with an increase in temperature. Irreversible quenching is generally related to a chemical dissociation or oxidation. Irreversible enhancements are generally related to thermal curing or passivation of the nanoparticle surface, generally resulting in an enhancement. Another possible cause of enhancement is thermoluminescence. Upon heating, carriers at some traps are released to the conduction band and contribute to the luminescence. As a result, the luminescence increases with increasing temperature. As the trapped sites are thermally emptied, the luminescence enhancement decreases in intensity. [0017] Shifts in emission energy, or equivalently wavelength, with temperature can be described by crystal field theory. The crystal field strength is enhanced at lower temperatures because the crystal lattice has physically contracted. As a consequence, the emitting state shifts to lower energies with decreasing temperature, shifting the emission to longer wavelengths. [0018] Variation of hydrostatic pressure can change the inter-atomic distance and the overlap among adjacent electronic orbitals. Pressure dependence of luminescence can provide useful information about the electronic state of an emitter and the interaction between the luminescence centers and their hosts. On the other hand, pressure can be measured though the measurement of luminescence changes. Nanoparticles, due to their size determined quantum confinement, present different pressure dependent luminescence properties than bulk materials and have great potential to be used for pressure sensing applications. [0019] In addition to single or single sized nanoparticles the present invention relates to a system composed of two or more nanoparticles of different sizes or with two or more different kinds of nanoparticles or one nanoparticle with two emitting centers. In these complex systems, there will be energy transfer from one nanoparticle (donor) to the other (acceptor) or from one emitter (donor) to the other (acceptor), by a process known as fluorescence resonance energy transfer (FRET). This energy transfer rate is inversely dependent on the 6.sup.th power of the distance between the donor and the acceptor. Thus, if the distance is changed slightly by varying temperature or pressure, the energy transfer rate will be changed greatly. As a result, the luminescence intensity and lifetime are related to temperature and pressure. Based on this theory, temperature or pressure sensors may be made with these systems. [0020] In addition to fluorescence, upconversion luminescence may have some advantages for temperature or pressure sensors as described in this invention. Upconversion luminescence is different from photoluminescence or fluorescence. In upconversion luminescence the excitation wavelength (energy) is longer (lower) than the emission wavelength (energy). This is opposite to what occurs in fluorescence or photoluminescence. Upconversion luminescence has many applications like energy upconversion, infrared imaging, biological labeling and displays. Strong upconversion luminescence has been observed in some nanoparticles. For example, two-photon-induced upconversion luminescence was first observed in ZnS:Mn.sup.2+ and ZnS:Mn.sup.2+,Eu.sup.3+ nanoparticles by one of the present inventors and such observations are reported in W. Chen, A. G. Joly, and J. Z. Zhang, Up-Conversion Luminescence of Mn.sup.2+ in ZnS:Mn Nanoparticles, Phys. Rev. B, 2001, 64, 0412021-4(R) and A. G. Joly, W. Chen, J. Roark, and J. Z. Zhang, Temperature dependence of Up-Conversion Luminescence of Mn.sup.2+ in ZnS:Mn Nanoparticles, Journal of Nanoscience and Nanotechnology, 2001, 1 (3):295-301. The observation revealed that the upconversion luminescence intensity of ZnS:Mn.sup.2+ nanoparticles is highly temperature dependent. One of the present inventors also observed a close-to-linear temperature dependence of the upconversion intensity in ZnS:Mn.sup.2+ nanoparticles formed in zeolite-Y. This observation is reported in A. G. Joly, W. Chen, J. Roark, and J. Z. Zhang, Temperature dependence of Up-Conversion Luminescence of Mn.sup.2+ in ZnS:Mn Nanoparticles, Journal of Nanoscience and Nanotechnology, 2001, 1 (3):295-301. This indicates that the upconversion luminescence of nanoparticles can be used in temperature sensors. One advantage of upconversion in temperature sensing or imaging is that the resolution or accuracy is better compared with fluorescence, because the emission background from the surroundings can be avoided in upconversion. This is particularly desirable in biological or biomedical applications, such as temperature monitoring during hyperthermia treatment of cancer. [0021] In addition, for upconversion luminescence other than two-photon absorption, an energy transfer process from donor to acceptor is very important. For electric multipolar interactions the energy transfer probability can be determined by the formula: P SA .function. ( R ) = ( R 0 / R ) S .tau. S where .tau..sub.S is the actual lifetime of the donor excited state, R.sub.0 is the critical transfer distance for which excitation transfer and spontaneous deactivation of the donor have equal probability, and R is the separation between the donor and the acceptor. s is a positive integer taking the following values: [0022] s=6 for dipole-dipole interactions [0023] s=8 for dipole-quadrupole interactions [0024] s=6 for quadrupole-quadrupole interactions The above theory indicates that donor-acceptor separation is a key parameter determining the energy transfer rate. From the above equation, it is known that the energy transfer rate is highly dependent on the separation between the donor and the acceptor. Different temperatures or pressures have different separations, and, of course, different transfer rates. As a result, upconversion luminescence efficiency and lifetime are different with different temperature and pressure. This is the basic concept behind upconversion temperature or pressure sensors. Continue reading... Full patent description for Nanoparticle thermometry and pressure sensors Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Nanoparticle thermometry and pressure sensors patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Nanoparticle thermometry and pressure sensors or other areas of interest. ### Previous Patent Application: Multi-site infrared thermometer Next Patent Application: Method and apparatus for generation of asynchronous clock for spread spectrum transmission Industry Class: Thermal measuring and testing ### FreshPatents.com Support Thank you for viewing the Nanoparticle thermometry and pressure sensors patent info. IP-related news and info Results in 1.58275 seconds Other interesting Feshpatents.com categories: Medical: Surgery , Surgery(2) , Surgery(3) , Drug , Drug(2) , Prosthesis , Dentistry |
||
